Difference between float and double in C/C++

For representing floating point numbers, we use float, double and long double.

What’s the difference ?

double has 2x more precision then float.

float is a 32 bit IEEE 754 single precision Floating Point Number1 bit for the sign, (8 bits for the exponent, and 23* for the value), i.e. float has 7 decimal digits of precision.

double is a 64 bit IEEE 754 double precision Floating Point Number (1 bit for the sign, 11 bits for the exponent, and 52* bits for the value), i.e. double has 15 decimal digits of precision.

Let’s take a example(example taken from here) :
For a quadratic equation x2 – 4.0000000 x + 3.9999999 = 0, the exact roots to 10 significant digits are, r1 = 2.000316228 and r2 = 1.999683772

// C program to demonstrate  
// double and float precision values 
  
#include <stdio.h> 
#include <math.h> 
  
// utility function which calculate roots of  
// quadratic equation using double values 
void double_solve(double a, double b, double c){ 
    double d = b*b - 4.0*a*c; 
    double sd = sqrt(d); 
    double r1 = (-b + sd) / (2.0*a); 
    double r2 = (-b - sd) / (2.0*a); 
    printf("%.5f	%.5f
", r1, r2); 
} 
  
// utility function which calculate roots of  
// quadratic equation using float values 
void float_solve(float a, float b, float c){ 
    float d = b*b - 4.0f*a*c; 
    float sd = sqrtf(d); 
    float r1 = (-b + sd) / (2.0f*a); 
    float r2 = (-b - sd) / (2.0f*a); 
    printf("%.5f	%.5f
", r1, r2); 
}    
  
// driver program 
int main(){ 
    float fa = 1.0f; 
    float fb = -4.0000000f; 
    float fc = 3.9999999f; 
    double da = 1.0; 
    double db = -4.0000000; 
    double dc = 3.9999999; 
  
    printf("roots of equation x2 - 4.0000000 x + 3.9999999 = 0 are :
"); 
    printf("for float values:
"); 
    float_solve(fa, fb, fc); 
  
    printf("for double values:
"); 
    double_solve(da, db, dc); 
    return 0; 
}   

/div>

Output:

roots of equation x2 - 4.0000000 x + 3.9999999 = 0 are : 
for float values: 
2.00000    2.00000
for double values: 
2.00032    1.99968

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Difference between float and double in C/C++

tags:

You Might Also Like

leave a comment

0 Comments

Subscribe to Our Newsletter

Top Followed books